This book explains the psychology theory behind design using plain language. The inspiration came from the "democratic design" philosophy of IKEA. This book attempts to help people enjoy designs more, by explaining consumer psychology that lurks behind designs of everyday things. Another purpose of the book is to aid designers and marketers in understanding consumer behavior and to help them leverage this knowledge in their respective fields. Marketers and designers often find it hard to communicate effectively due to their disparate fields. However, this book aims to bridge this gap by showing that activities in both design and marketing can be better understood through the lens of design psychology, promoting better communication and collaboration. Although the book contains more than a hundred psychology theories that can affect design, it is structured in a reader-friendly manner, and chapters are segmented such that each chapter contains about 7~15 theories. Despite the large amount of academic research behind the theories, the application of these theories comes from commonplace consumer behaviors and daily design examples, promising an easy, relatable read.